This project will investigate the epidemiologic and immunologic aspects of infections in drug abusers. To start with, the source of infection of narcotics addicts with staphylococcus aureus is being investigated. Preliminary data show that actively injecting addicts have a markedly increased carrier rate of S. aureus in the nose and throat. The reason for this will be sought by looking at epidemiologic data about these patients and at their immune status as regards the staphylococcus. Specifically studies of humoral and cell-mediated immune mechanisms against staphylococci will be investigated.